Antifouling paints



rpury mw UNIT FFICE ANTIFOULING PAINTS Davis A. Skinner, Compton, and Thomas F. Doumani, Los Angeles, Calif., assignors to Union Oil Company of California, Los Angeles, Calif., a corporation of California No Drawing. Application February 7, 1949, Serial No. 75,096

This invention relates to anti-fouling paints, and in particular concerns coating compositions adapted to protect wood or metal surfaces to which they are applied from the accumulation of marine organisms.

In the construction and maintenance of structures exposed to marine waters, e. g. ship hulls, wharves, and the like, it is common practice to paint such structures with a so-called anti-fouling paint for the purpose of preventing or inhibiting the accumulation of various types of marine organisms on said structures. Such paint may be the only protective coating provided, but more usually it is applied over one or more priming coats of paint more suitably adapted to protect the structure from corrosion and the like. The anti-fouling paints at present in use for the most part comprise a paint base to which has been added one or a combination of materials toxic to lower forms of life. Various compounds of mercury, arsenic, and copper, and combinations of such compounds are widely used for this purpose, but are not entirely satisfactory, either by reason of the large amounts in which they must be employed or by reason of their relatively high cost.

It is accordingly an object of the present invention to provide improved coating compositions capable of preventing or inhibiting the growth of marine organisms, such as algae, barnacles and other forms of marine life.

Another object is to provide paint compositions suitable for application to wooden or. metal ship hulls, wharves, and other structures exposed to marine waters for the purpose of protecting such structures from becoming fouled with marine growths.

A further object is to provide anti-fouling paints comprising new and improved anti-fouling agents.

Other and related objects will be apparent from the following detailed description of the invention.

We have now found that the above objects and attendant advantages may be realized in paint compositions containin as an anti-fouling agent a copper salt of a lower alkyl mercaptan, e. g. cuprous methyl mercaptide, cuprous isopropyl mercaptide, cupric sec-butyl mercaptide, etc. More particularly, we have found that paint compositions comprising in addition to the usual oily and/or resinous vehicle, pigment and/or filler, drier, thinner, etc., a minor proportion of one or a mixture of copper lower alkyl mercaptides have a strong inhibiting effect on the growth of vari- L; V i

8 Claims. (01. 106-15) one marine organisms, and are hence admirably suited for application to surfaces submerged in water. The copper mercaptide compounds do not appreciably affect the original desirable qualities of a paint, and accordingly the composition provided by the invention may, if desired, be prepared simply by adding the requisite amount of the desired copper mercaptide compound to any commercial water-resistant paint. The copper salts of higher alkyl and aromatic mercaptans may be similarly, although less preferably, employed as anti-fouling agents.

The copper salts of lower alkyl mercaptans, referred to herein as copper lower alkyl mercaptides, are conveniently obtained by reaction between 2, lower alkyl mercaptan, i. e., an alkyl mercaptan containing from 1 to 7 carbon atoms; and a copper salt of a weak acid, e. g., cupric acetate. The reaction may be carried out simply by adding the mercaptan, either as such or dissolved in an inert solvent such as ethanol, benzene, etc., to an aqueous solution of copper acetate with stirring at room temperature. The copper mercaptide product precipitates out of solution and is filtered off, washed with an organic solvent such as benzene, ethanol, ether, etc., and dried. Alternatively, the aqueous copper salt may be added to the mercaptan. The copper mercaptides may also be prepared by a metathesis reaction between an aqueous sodium lower alkyl mercaptide and an aqueous copper salt such as cupric sulfate.

As previously mentioned, the copper lower alkyl mercaptides may be employed in the new paint compositions as individual compounds or in admixture with one another. In the latter instance any of the individual copper lower alkyl mercaptides may be admixed, or the mixed mercaptides may be prepared directly by reaction between a copper salt and a mixture of lower alkyl mercaptans as previously described. A particularly suitable mixture of lower alkyl mercaptans for this purpose is the mercaptan mixture obtained as a by-product in the so-called Unisol process of petroleum refining. Such process consists essentially in the extraction of naturally occurring mercaptans from petroleum distillates with the aid of a solvent comprising aqueous sodium hydroxide and methanol. Upon stripping the extract phase with steam, the mercaptans originally present in the petroleum distillate are recovered as a mixture of lower alkyl mercaptans distilling over the range of from about F. to about 300 F. and comprising alkyl mercaptans containing from 3, to about '7, carbons and a small amount of Approximately 100 parts of sec-butyl mercaptan was dissolved in about 800 parts of benzene and added with stirring to a solution of 200 parts of cupric acetate in 3500 parts of water. The mixture was stirred at room temperature for several hours, after which the orange-yellow precipitate which had formed was filtered off and washed successively with water, benzene, ethanol, and ether. After drying overnight in a vacuum desiccator, the product weighed 125 parts and had an ultimate analysis corresponding to cuprous sec-butyl mercaptide, SEC-C4H9S-CU.

Example II By means of procedure similar to that described in Example I, the following copper lower alkyl mercaptides were prepared:

Copper methyl mercaptide Copper ethyl mercaptide Copper propyl mercaptide Copper iso-propyl mercaptide Copper butyl mercaptide All of these products were yellow to brown finelydivided solids, suitable for use according to the present invention. By analogous procedure, other copper lower alkyl mercaptides, e. g. copper iso-butyl mercaptide, copper n-amyl mercaptide, mixed copper hexyl mercaptides, etc., may be obtained.

Example III Approximately 88 parts of a mixture of lower alkyl mercaptans, obtained by the Uniso-l refining of a cracked petroleum distillate and comprising alkyl mercaptans containingfrom 1 to about 7 carbon atoms and a small amount of liquid hydrocarbons, was dissolved in about 220 parts of ethanol. This solution was added slowly with stirring at room temperature to 82 parts of cupric acetate dissolved in 1200 parts of water. A bright yellow precipitate formed immediately. This product was filtered off, washed with water and acetone, and dried. Treatment of the mother liquor with an additional quantity of the mercaptan solution yielded an additiona1 small amount of the yellow precipitate. Analysis showed the product to consist of mixed cupric alkyl mercaptides, R-S-CU--SR., wherein R is an alkyl group containing from 1 to 7 carbon atoms.

In addition to the copper mercaptide antifouling agent, the paint compositions provided by the invention essentially comprise the usual vehicle or binder, igment and thinner. It may, of course, contain various optional ingredients, such as driers, pigment extenders, anti-foaming agents, anti-corrosion agents, and supplementary anti-fouling agents. The vehicle or binder may suitably be a varnish-type of composition, e. g. a cooked combination of natural or synthetic drying oils and natural or synthetic resins, a Wide variety of which are available in different oil lengths and embodying various combinations of oils and resins. Alternatively, the vehicle may comprise merely a drying oil, such as raw or boiled linseed oil, tung oil, etc., to which driers such as cobalt or manganese linoleate or naphthenate may be added. It may also be of a bituminous nature embodying for example, a bituminous material such as asphalt in cooked combination with a drying oil. In general, it may be stated that any of the vehicles or binders employed in formulating exterior paints and finishes may be employed as such in the present compositions.

The pigments and extenders employed in the new compositions may likewise be any of those commonly employed in exterior paints and finishes, although it is preferable to employ those which are considered to have anti-corrosive properties, e. g. lead chromate, zinc chromate, red lead, iron oxide, zinc oxide, zinc powder, etc. Other types of pigments such as white lead, lithopone, blanc fixe, lead sulfate, titanium dioxide, zinc oxide, zinc sulfide, leaded zinc oxide, etc., and various extenders, such as silica, magnesium silicate, whiting, calcium carbonate, barytes, etc., and various combinations of pigments and extenders may likewise be employed.

Similarly, any of the commonly employed thinners may be used, e. g. turpentine, mineral spirit, light naphtha, various synthetic solvents, etc.

The following examples of representative paint compositions will illustrate a number of ways in which the principle of the invention has been applied, but are not to be construed as limiting the same.

Example IV Shellac varnish gallons 15 Zinc oxide pounds 30 Blanc fixe do 10 Indian red do 50 Pine tar gallons 8 Denatured alcohol do 10 Turpentine d0 8 Copper ethyl mercaptide pounds 50 Example V Alkali-refined linseed oil -gallons 12 Boiled linseed oil do 1 Red lead "pounds" 25 Zinc oxide do 50 Cobalt linoleate do 0.2 Silica do 15 Mineral spirits gallons 12 Copper iso-propyl mercaptide pounds 40 Example VI Marine paint base gallons 6 Zinc oxide pounds 20 India red do 5 Magnesium silicate do 3 Silica do 3 Mixed copper lower alkyl mercaptides pounds.. 15

The marine paint base is a commercial asphaltbase varnish thinned with mineral spirits.

Example VII Commercial heavy duty anti corrosion paint "gallons.- 10

Coppe n-butyl mercaptide pounds 20 Turpentine r gal1ons 0.5

Example VIII Tung oil "gallons; 3 Linseed oil do 3 Cumarone resin pounds 100 Zinc oxide do 25 Barytes do 125 VMP naphtha gallons 25 Copper methyl mercaptide pounds 100 Example IX 45-gal. spar varnish g-allons Zinc tertiary chromate pounds 125 Pine tar gallons 5 Mineral spirits do 5 Mixed copper lower alkyl mercaptides pcunds 50 Example X 8-gal. tung-linseed oil phenolic varnish gallons 10 Red lead pounds 150 Mineral spirits gallons 3 Copper hexyl mercaptides pounds 40 It will be apparent from the preceding examples that the paint base in which the copper mercaptide anti-fouling agent is incorporated may take a wide variety of forms. In general, it is preferable that the vehicle or binder be an asphalt-base varnish or a medium oil-length spar varnish. Similarly, it is preferable that the pigment comprise at least one material having anticorrosion properties. The pigment-to-vehicle ratio may vary widely but is preferably between about l/1 and about 3/1 in accordance with usual practice. The nature of the thinner and the content thereof may be varied to secure desired viscosity and drying characteristics. Usually, paints of this type are applied by brush, and the viscosity will be adjusted accordingly, although they may be prepared for spray application if desired. The copper lower alkyl mercaptide anti-fouling agent is employed in an amount suflicient to inhibit the normal tendency of the base paint to become fouled by marine organisms when applied to surfaces exposed to water. Such amount will usually be between about 10 and about 30 per cent by weight of the entire composition depending upon the composition of the base paint and the fouling conditions to which the paint film is subjected.

The new paint compositions may be applied in any conventional manner, i. e., they may be applied directly to the surface to be protected, or they may be applied over one or more priming coats. If desired, an asphalt undercoat may be employed as described in U. S. Patent 2,364,460. The nature and composition of suitable primers and undercoats is well understood in the art.

The following example presents quantitative data on the effectiveness of several copper lower alkyl mercaptides as the anti-fouling agent in a typical paint composition of the present class, but is not to be construed as limiting the same.

Eaample XI A base paint of the following composition was prepared:

Marine paint base gallons 13 Zinc oxide "pounds" 40 India red do 10 Magnesium silicate do 6 Silica d0 6 The marine paint base was an asphalt-base Varnish diluted to a thin liquid with mineral spirits.

The ingredients were blended to form a thin paint having a density of 1.33 g./ml. Various copper lower alkyl mercaptides were then ground into separate portions of the base paint in such amount that the final composition contained 20 per cent by weight of the copper mercaptide (about 10 per cent by weight of copper as metal). The resulting compositions were then applied to white pine panels mounted on a frame-work adapted to be lowered into the sea at right angles to the prevailing current. Each paint composition was applied to one-half of the surface area on both sides of each respective panel; the other half was painted with the base paint alone and served as a control. In addition to the panels coated with the compositions containing copper lower alkyl mercaptides, one panel was coated with a commercial antifouling paint which contained a high proportion of copper, mercury, and arsenic compounds as anti-fouling agents. This panel served as a basis for comparison. The panels were completely submerged in the seat for sixty days, after which they were removed and examined for fouling by marine growth. Each panel was rated on an arbitrary scale of zero to 5, zero representing no growth and 5 representing the growth on the unpainted portion of the panels.

Foulin Paint No. Anti-Fouling Agent Rating 60-Day Copper methyl mercaptide 0 Copper ethyl mercaptide 0i Copper n-propyl mercaptide. 1.5 Copper iso-propyl mercaptide. 2+ Copper n-butyl mercaptide. 0+ go per scc-bgiyl nl lercaptilzigen 0+ c. l per cen n, gay s, as me 0 mecumrol).:.;--.. :ti f?k--- 5 gommercial'a'nt i iouling paint.

It will be noted from the above data that all of the compositions were highly superior to the control, and compared Very favorably with the commercial product which contained more than twice the quantity of anti-fouling agents considerably more costly than those of the present class.

Other modes of applying the principle of our invention may be employed instead of those explained, change being made as regards the methods or materials herein disclosed provided the product stated by any of the following claims, or the equivalent of such stated product, be obtained.

We, therefore, particularly point out and claim as our invention:

1. An anti-fouling paint composition comprising a paint which is normally subject to foulin by marine organisms when applied to surfaces exposed to marine waters and a copper alkyl mercaptide having from 1 to 7 carbon atoms in an amount sufllcient to inhibit said fouling.

2. A composition according to claim 1 wherein the copper alkyl mercaptide is present in an amount representing from about 10 to about 30 per cent by weight of the entire composition.

3. A composition according to claim 1 wherein the copper alkyl mercaptide is copper n-butyl mercaptide.

4. A composition according to claim 1 wherein the copper alkyl mercaptide is copper sec-butyl mercaptide.

5. A composition according to claim 1 wherein the copper alkyl mercaptide is in admixture with other copper alkyl mercaptides containing from 1 to '7 carbon atoms.

6. An anti-fouling paint composition comprising a paint vehicle, suflicient pigment material to providea; 'pigm'ent-to-vehicle ratio of from about 1/1 to about 3/1, sufficient paint thinner to secure brushing consistency, and from about 10 to about 30 per cent by weight of a co per alkyl n ercap tide having from 1 to 7 carbon a ms "l. The composition of claim 6 wherein the w THOMAS F. DOUMANI. 15

REFERENCES CITED UNITED STATES PATENTS Number Name Date 2,217,358 Coltof Oct. 8, 1940 2,346,102 De Simo et a1 Apr. 4, 1944 2,390,408 Young Dec. 4, 1945 OTHER REFERENCES Antifouling Paints, Industrial and Engineering Chemistry, vol. 37, N0. 5, page 461. 

1. AN ANTI-FOULING PAINT COMPOSITION COMPRISING A PAINT WHICH IS NORMALLY SUBJECT TO FOULING BY MARINE ORGANISMS WHEN APPLIED TO SURFACES EXPOSED TO MARINE WATERS AND A COPPER AKLYN MERCAPTIDE HAVING FROM 1 TO 7 CARBON ATOMS IN AN AMOUNT SUFFICIENT TO INHIBIT SAID FOULING. 